In the field of lubricating oils, additives such as pour point depressants have conventionally been added to lubricating base oils including highly refined mineral oils, to improve the cold properties of the lubricating oils (see Patent documents 1-3, for example). Known processes for production of high-viscosity-index base oils include processes in which stock oils containing natural or synthetic normal paraffins are subjected to lubricating base oil refining by hydrocracking/hydroisomerization (see Patent documents 4-6, for example).
The indexes for evaluating the cold properties of lubricating base oils and lubricating oils are generally the pour point, cloud point and freezing point.